Octave图片转游戏代码脚本报错：rgb2gray不支持logical类型RGB

问题 #

运行Octave图片转游戏代码脚本时，处理1507.png时报错：

error: rgb2gray: RGB of invalid data type 'logical'
error: called from
colorspace_conversion_input_check at line 41 column 7
rgb2gray at line 61 column 5
FreeRiderImageMaker at line 31 column 15

重复运行、调整originY参数均无法解决，原脚本如下：

% The images must be in the same folder as this script.
% The originY variable will be updated for each PNG file.
originY = 3010000;

% Threshold values modify which shades of grey are consirered scenery (0-255).
threshold1 = 50; %black is 0
threshold2 = 0; %white is 255

% The origin modifies where the rider begins relative to the image.
originX = 200;

% Images can be made larger using the scale option. Use only whole numbers.
% Note that there is a size limit for tracks uploaded to FRHD.
scaleX = 2;
scaleY = 2;

% Loop through each PNG file until 2154.png.
for n = 1505:2154
    % Create the file name for the current PNG file.
    filename = sprintf('%04d.png', n);

    % Read the PNG file.
    image = imread(filename);

    % Create the file name for the output text file.
    outputFilename = sprintf('%04d.txt', n);

    % Open the output text file for writing.
    output = fopen(outputFilename, 'w');

    grayImage = transpose(rgb2gray(image));
    sceneryString = sprintf('#');

    for j = 1:(size(grayImage,2)*scaleY)
        currentColor = 2; % 2 for white, 1 for gray, 0 for black
        for i = 1:size(grayImage,1)
            if originY+j >= 0
                row = lower(dec2base(originY+j, 32));
            else
                row = strcat('-', lower(dec2base(-(originY+j), 32)));
            end;

            if originX+i*scaleX >= 0
                xPos = lower(dec2base(originX+i*scaleX, 32));
            else
                xPos = strcat('-', lower(dec2base(-(originX+i*scaleX), 32)));
            end;

            pixel = grayImage(i,ceil(j/scaleY));

            if currentColor == 2
                if pixel > threshold2
                    continue;
                elseif pixel < threshold1
                    fprintf(output, '%s %s ', xPos, row);
                    currentColor = 0;
                else
                    sceneryString = sprintf('%s%s %s ', sceneryString, xPos, row);
                    currentColor = 1;
                end;
            elseif currentColor == 0
                if pixel < threshold1
                    continue;
                elseif pixel > threshold2
                    fprintf(output, '%s %s,', xPos, row);
                    currentColor = 2;
                else
                    fprintf(output, '%s %s,', xPos, row);
                    sceneryString = sprintf('%s%s %s ', sceneryString, xPos, row);
                    currentColor = 1;
                end;
            else
                if pixel > threshold2
                    sceneryString = sprintf('%s%s %s,', sceneryString, xPos, row);
                    currentColor = 2;
                elseif pixel < threshold1
                    sceneryString = sprintf('%s%s %s,', sceneryString, xPos, row);
                    fprintf(output, '%s %s ', xPos, row);
                    currentColor = 0;
                else
                    continue;
                end;
            end;
        end;

        if currentColor == 1
            sceneryString = sprintf('%s%s %s,', sceneryString, xPos, row);
        elseif currentColor == 0
            fprintf(output, '%s %s,', xPos, row);
        end;
    end;
    sceneryString = sprintf('%s#', sceneryString);
    fprintf(output, '%s', sceneryString);
    fclose(output);

    % Increase the value of originY by 2000 for the next iteration of the loop.
    originY = originY + 2000;
end;

解决方案 #

核心原因 #

1507.png是单通道灰度图/二值图，imread读取后返回logical类型数组（而非RGB三通道数组），但rgb2gray仅支持输入RGB格式图像，因此触发类型不匹配报错。

修复方案 #

在调用rgb2gray前增加图像格式判断，对单通道图像直接做格式转换，无需调用rgb2gray。修改后的完整脚本如下：

% The images must be in the same folder as this script.
% The originY variable will be updated for each PNG file.
originY = 3010000;

% Threshold values modify which shades of grey are consirered scenery (0-255).
threshold1 = 50; %black is 0
threshold2 = 0; %white is 255

% The origin modifies where the rider begins relative to the image.
originX = 200;

% Images can be made larger using the scale option. Use only whole numbers.
% Note that there is a size limit for tracks uploaded to FRHD.
scaleX = 2;
scaleY = 2;

% Loop through each PNG file until 2154.png.
for n = 1505:2154
    % Create the file name for the current PNG file.
    filename = sprintf('%04d.png', n);

    % Read the PNG file.
    image = imread(filename);

    % --- 新增：兼容单通道/逻辑型图像 ---
    if ndims(image) <= 2
        % 单通道图像直接转为uint8格式（二值图自动映射为0/255）
        grayImage = transpose(uint8(image));
    else
        % RGB三通道图像正常转灰度图
        grayImage = transpose(rgb2gray(image));
    end
    % --- 新增结束 ---

    % Create the file name for the output text file.
    outputFilename = sprintf('%04d.txt', n);

    % Open the output text file for writing.
    output = fopen(outputFilename, 'w');

    sceneryString = sprintf('#');

    for j = 1:(size(grayImage,2)*scaleY)
        currentColor = 2; % 2 for white, 1 for gray, 0 for black
        for i = 1:size(grayImage,1)
            if originY+j >= 0
                row = lower(dec2base(originY+j, 32));
            else
                row = strcat('-', lower(dec2base(-(originY+j), 32)));
            end;

            if originX+i*scaleX >= 0
                xPos = lower(dec2base(originX+i*scaleX, 32));
            else
                xPos = strcat('-', lower(dec2base(-(originX+i*scaleX), 32)));
            end;

            pixel = grayImage(i,ceil(j/scaleY));

            if currentColor == 2
                if pixel > threshold2
                    continue;
                elseif pixel < threshold1
                    fprintf(output, '%s %s ', xPos, row);
                    currentColor = 0;
                else
                    sceneryString = sprintf('%s%s %s ', sceneryString, xPos, row);
                    currentColor = 1;
                end;
            elseif currentColor == 0
                if pixel < threshold1
                    continue;
                elseif pixel > threshold2
                    fprintf(output, '%s %s,', xPos, row);
                    currentColor = 2;
                else
                    fprintf(output, '%s %s,', xPos, row);
                    sceneryString = sprintf('%s%s %s ', sceneryString, xPos, row);
                    currentColor = 1;
                end;
            else
                if pixel > threshold2
                    sceneryString = sprintf('%s%s %s,', sceneryString, xPos, row);
                    currentColor = 2;
                elseif pixel < threshold1
                    sceneryString = sprintf('%s%s %s,', sceneryString, xPos, row);
                    fprintf(output, '%s %s ', xPos, row);
                    currentColor = 0;
                else
                    continue;
                end;
            end;
        end;

        if currentColor == 1
            sceneryString = sprintf('%s%s %s,', sceneryString, xPos, row);
        elseif currentColor == 0
            fprintf(output, '%s %s,', xPos, row);
        end;
    end;
    sceneryString = sprintf('%s#', sceneryString);
    fprintf(output, '%s', sceneryString);
    fclose(output);

    % Increase the value of originY by 2000 for the next iteration of the loop.
    originY = originY + 2000;
end;

额外说明 #

• 如果1507.png是二值图（仅0和1），转为uint8后会自动转为0和255，完全符合脚本中阈值判断逻辑（0为黑，255为白），无需调整阈值参数。
• 该修改同时兼容后续所有单通道格式的PNG图片，避免再次出现同类报错。

内容的提问来源于stack exchange，提问作者Labebeh